This invention pertains to an image projection arrangement for projection enlarged three-dimensional images of objects into space for viewing by observers.
Image projection from transparencies onto flat or curved surfaces or onto screens is well known. For example, U.S. Pat. No. 3,293,982 to Appeldorn and U.S. Pat. No. 3,340,765 to Herriott disclose systems for overhead projection of images from a transparency onto a displaced screen, whereby light is transmitted through the transparency, then reflected back and projected onto the screen. However, these devices project only flat two-dimensional images. U.S. Pat. No. 1,866,870 to O'Neill discloses an apparatus which projects a three-dimensional form, but it provides only minor magnification or enlargement of the image and has a limited viewing zone. Also, U.S. Pat. No. 3,293,983 to Gaudyn discloses a display device utilizing a parabolic mirror and conventional Fresnel lens to project a three-dimensional image of an object into space for side viewing.
A spherical lens, when the diameter is large and surpasses the radius of curvature, becomes bulky. Since refraction is accomplished at the surfaces, the major spherical part can be removed and a conventional Fresnel lens is thereby constructed. A conventional Fresnel lens is a flat thin piece of glass or plastic in which are molded a series of small concentric stepped zones extending from center to outer margin. Each groove provides a minute refracting facet capable of bending light.